1. Field of the Invention
The present invention relates to a mechanism for adjusting the resonance frequency of a dielectric resonator having TE.sub.01.delta. mode under the presence of electromagnetic field.
2. Description of the Related Arts
In recent years, dielectric resonators which oscillates in TE.sub.01.delta. mode are used in the local oscillator of a down-converter for converting a radio wave signal, transmitted from a satellite and received by an antenna, into a signal of a low frequency. An example of a conventional dielectric resonator of this kind is shown in FIG. 3.
The dielectric resonator 1 is cylindrical and made of a dielectric material having a high dielectric constant. The dielectric resonator 1 is adhered with resin or glass to a support 2 made of ceramic having a low dielectric constant. The dielectric resonator 1 and the support 2 are accommodated in a metal case 3 accommodating the local oscillator of the down-converter of a satellite broadcasting receiver not shown.
In addition to the function of supporting the dielectric resonator 1, the support 2 resonates the dielectric resonator 1 in TE.sub.01.delta. mode in the metal case 3 and adjusts the coupling between the dielectric resonator 1 and circuits (not shown) composing the oscillator of the down-converter.
The resonance frequency f.sub.0 of the dielectric resonator 1 is determined by parameters such as the relative dielectric constant (.epsilon..sub.r) of a dielectric material composing the dielectric resonator 1, the dimension thereof, the supporting position of the dielectric resonator 1 in the metal case 3, and the inner dimension of the metal case 3.
However, the parameters have deviations in manufacturing the oscillator of the down-converter for the satellite broadcasting receiver, and consequently, the resonance frequency f.sub.0 of the dielectric resonator 1 also has deviations.
The dielectric resonator 1 has the following construction for adjusting the resonance frequency f.sub.0 so that the resonance frequency f.sub.0 has a predetermined value.
That is, a through hole 4 is formed in the upper wall of the metal case 3 in opposition to the upper surface of the dielectric resonator 1 and a metal tuning screw 5 is inserted into the hole 4 as shown in FIG. 3. The resonance frequency f.sub.0 is adjusted to have a uniform value by changing the insertion amount (d) of the tuning screw 5 into the hole 4.
The conventional mechanism for adjusting the resonance frequency of the dielectric resonator has a problem that when the interval between the tuning screw 5 and the dielectric resonator 1 becomes small in inserting the tuning screw 5 toward the dielectric resonator 1, the tuning screw 5 approaches a region in which the intensity of the electric field enclosed in the dielectric resonator 1 and in the vicinity thereof in the metal case 3 is great. As a result, conductor loss increases and thus the unloaded Q(Qu) of the dielectric resonator 1 drops.